linux-kernel - Re: [PATCH v2 1/2] Revert "locking/rwsem: Remove reader optimistic spinning"

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Message-ID: <ZPYr4z/h2lZLtqoZ@gmail.com>
Date:   Mon, 4 Sep 2023 21:11:31 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Bongkyu Kim <bongkyu7.kim@...sung.com>, mingo@...hat.com,
        will@...nel.org, longman@...hat.com, boqun.feng@...il.com,
        linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: [PATCH v2 1/2] Revert "locking/rwsem: Remove reader optimistic
 spinning"


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, Sep 01, 2023 at 10:07:03AM +0900, Bongkyu Kim wrote:
> > This reverts commit 617f3ef95177840c77f59c2aec1029d27d5547d6.
> > 
> > In mobile environment, reader optimistic spinning is still useful
> > because there're not many readers. In my test result at android device,
> > it improves application startup time about 3.8%
> > App startup time is most important factor for android user expriences.
> > So, re-enable reader optimistic spinning by this commit. And,
> > the later patch will make it optional feature by cmdline.
> 
> I'm not seeing any mention on how this interacts with all the rwsem work
> that has been done since that commit, like the handoff rework.
> 
> Why is a straight revert a sane thing at this point?

Yeah, so this should probably be titled:

   locking/rwsem: Reintroduce reader optimistic spinning

... instead of the double-negative 'remove removal' thing that is indeed 
confusing.

Thanks,

	Ingo